.\" Copyright (c) 2001
.\"	The FreeBSD Project
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd July 11, 2020
.Dt NMDM 4
.Os
.Sh NAME
.Nm nmdm
.Nd nullmodem terminal driver
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device nmdm"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
nmdm_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides two
.Xr tty 4
devices connected
by a virtual
.Dq "null modem"
cable.
.Pp
If either of the two tty devices have the
.Dv CDSR_OFLOW
bit
.Pq Dq Li "stty dsrflow"
set in their line discipline, the
.Nm
device will emulate the speed configured in the
.Xr termios 4
settings.
The speed emulation works independently in the two directions,
controlled by the slower end's termios settings
.Va ( c_ispeed , c_ospeed ,
.Dv CS5 ... CS8 , CSTOPB
and
.Dv PARENB ) .
.Sh FILES
.Bl -tag -width ".Pa /dev/nmdm Ns Ar N Ns Op Pa AB" -compact
.It Pa /dev/nmdm Ns Ar N Ns Op Pa AB
nullmodem device nodes.
Where the
.Pa A
node has a matching
.Pa B
node.
.El
.Pp
The
.Nm
driver implements
.Dq "on-demand device creation"
so simply accessing a given instance in
.Pa /dev
will create it.
.Sh DIAGNOSTICS
None.
.Sh SEE ALSO
.Xr stty 1 ,
.Xr termios 4 ,
.Xr tty 4 ,
.Xr ttys 5
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 4.4 .
